1. Field of Invention
The invention relates generally to trimming circuit and, more particularly, the invention relates to trimming circuit for trimming a packaged IC chip.
2. Description of Related Art
During the fabricating processes of an integrated circuit (IC), electrical characteristics of the IC may drift due to the deviations of the processes. For example, the output voltage is originally intended to be 1.3V, but finally may be measured to be 1.35V or 1.25V due the deviations of the process. The drift of electrical characteristics causes uncertainties in designing the circuits. Therefore, in order to eliminate factors causing electrical drift, besides the continuous progress on the manufacturing process of IC, the trimming technique can be adopted to adjust the drifted electrical characteristics.
The conventional trimming technique includes a current trim or a laser trim method. For example, in the laser trim technique, a laser beam is used to cut at least one wire of the circuit to be trimmed. The electrical characteristics of the circuit to be trimmed are adjusted by cutting some wire and leaving the other(s). However, it is acquired additional equipment to perform laser-cut trimming for the IC, and thus the hardware cost is increased. Moreover, the electrical characteristics may be further drifted after the circuits being packaged as an IC chip. And the conventional trimming technique is not applicable to the packaged IC chip.
Refer to FIG. 1. FIG. 1 is a block diagram of a conventional packaged IC chip 50. The conventional packaged IC chip 50 has a plurality of pads 52 and a core circuit 54. The core circuit 54 is packaged in the IC chip 50 and electrically connected to the pads 52. Since the core circuit 54 is packaged, it is difficult to adjust the drifted electrical characteristics of the core circuit 54.